CVE-2026-89564

In the Linux kernel, the following vulnerability has been resolved:

ip: orphan prefetched skbs before multicast forwarding

IPv4 and IPv6 input preserve an skb->sk association installed by bpf sk assign() so that local delivery can use the selected socket under RCU. Both address families can also prefetch a socket in UDP early demux. In both paths (BPF and UDP early demux) a reference is not guaranteed to be held on the socket.

When a multicast packet is not locally deliverable, IPv6 hands the original skb to ip6 mr input(). IPv4's ip mr input() similarly keeps the original skb when local delivery is not needed. Either path can put the skb on an unresolved multicast route queue or forward it after the receive-side RCU section ends.

After the prefetched socket is destroyed, a later skb free invokes sock pfree() and dereferences the stale skb->sk. Orphan the skb before each non-local multicast forwarding path. Local delivery retains the original skb; the existing skb clone() calls provide multicast forwarding with a socket-free clone.